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Introduction to GIS
Definition and Components of GIS
Lecture Outline
• What is GIS?
• Evolution of GIS
• Elements of A GIS
• The scope of GIS
• Data Structures
Definition and Components of GIS
G eographic
I nformation
S ystem
Definition and Components of GIS
GEOGRAPHIC
• GEO - physical aspects
- socio-demographic aspects
- artificial aspects
*all with fixed locations (coordinates)
Definition and Components of GIS
GEOGRAPHIC
• GRAPHIC - does not refer to graphic
representations like maps
- refers to description of the
earth and what is upon it
- described in a digital model (3D)
which allows visualization at any
possible point of view
- presentation of processed data in
the form of one or more maps
Definition and Components of GIS
INFORMATION
• "communication of knowledge"
• a GIS provides information
• by itself, a GIS does not contain information
• a GIS makes information - by processing data
already entered
Definition and Components of GIS
SYSTEM
• Regularly interacting group of items
forming a unified whole.
Definition and Components of GIS
GIS
A computer system for
capturing, managing,
integrating, manipulating,
analyzing and displaying
data spatially referenced.
-Donnell & Kemp, 1995
Definition and Components of GIS
EVOLUTION OF A GIS
-evolved from different fields in which development has
led to the GIS as we now know it.
• cartography (high quality drafting)
• CAD / computer graphics
• surveying
• remote sensing
• computer technology (made it affordable)
Definition and Components of GIS
Geographical data describes
objects from the real world...
• position w/ respect to a known coordinate
system
• their attributes (e.g. pH, color, cost, etc.)
• their spatial interrelations w/ each other
(topological relations), which describe how
they are linked or how one can travel
between them
Definition and Components of GIS
Items in a GIS are classified into
separate components….
•degree of hardness or
tangibility
•position in the data
flow
Definition and Components of GIS
According to
Hardness or Tangibility
• hardware
• software
• orgware
Definition and Components of GIS
HARDWARE
• micro pc - at least a 486DX with minimum
16 megabytes ram, 1 GB hard disk with
color monitor (at least 256 colors)
• scanner and /or digitizer
• inkjet printer and/or plotter
• any large data storage device
Definition and Components of GIS
SOFTWARE
• IDRISI • MAPINFO
• ILWIS • OZ-GIS
• ARCVIEW • ER MAPPER
• PC ARCINFO • GRASS
• ATLAS
Definition and Components of GIS
ORGWARE
• organization about the use of hardware and
software
• man, their methods and organization
• “education and training” of staff at all levels
Definition and Components of GIS
According to
POSITION IN DATA FLOW
• input
• storage /management
• processing, manipulation and
analysis
• output
Definition and Components of GIS
DATA…DATA…DATA
• valid output needs a valid input - expensive
• collect only needed data but due to expense
in collection, the data should also be
multipurpose, ie., it can still be used by
unrelated independent users
• data exchange - standards are needed
• data quality - the potential error should be
measurable
Definition and Components of GIS
DATA COST vs DATA QUALITY
DATA COST
0
0% DATA QUALITY 100%
Definition and Components of GIS
3 components of geographic data
• the phenomenon being reported (physical
dimension or class) e.g., live coral cover,
height of forest canopy, population of a
settlement, width of a road
• spatial component - represented on a map as
either a point, line or area.
• time - not stated explicitly, but often critical
Definition and Components of GIS
DATA INPUT
• involves also converting data (analog to
digital)
• typically the major bottleneck
• GIGO, so checking for inaccuracies is very
important
• input methods and standards must be
considered first before data entry
Definition and Components of GIS
DATA MANAGEMENT
• storing and retrieving data
• method implemented affects the efficiency
of the system
• also involves organization of data - its
structure and relationships determine how
data is accessed and the speed of the
retrieval
Definition and Components of GIS
DATA ANALYSIS
• determines the information that can be
generated
• introduction of a GIS will not only
automate, it will also change the way an
organization works
Definition and Components of GIS
DATA OUTPUT
• maps
• tables
• text
Definition and Components of GIS
GIS Planning
Process
Definition and Components of GIS
SCOPE OF GIS
(a specific purpose)
• spatial analysis
• spatial planning
• implementation of plans
• spatial management
Definition and Components of GIS
SPATIAL ANALYSIS
• starts with a description of the situation at a
given moment (point-in-time measurement
which may not be sufficient particularly if
the purpose is to gain insight as to how the
situation develops in the future)
Definition and Components of GIS
SPATIAL ANALYSIS
(a “simplistic” case)
• assume coral reef susceptibility to man-induced
destruction is determined by:
– availability of materials for blast fishing
– population density of dynamite fishermen
• it is the relationships between these factors that
determines reef areas most susceptible to man-induced
destruction
Definition and Components of GIS
The Problem
Find coral reef areas in
Cebu that have the lowest
potential for success in
coral reef conservation.
Definition and Components of GIS
What data do we need?
• coral coverage - map of coral coverage (MAP 1)
• availability of materials for blast fishing - map
showing locations of large mango plantations
(MAP 2)
• density of dynamite fishermen - map showing
population densities of dynamite fishers in coastal
areas (MAP 3)
Definition and Components of GIS
How do we analyze the data?
• Map 1 - show areas with >50% live coral
coverage
• Map 2 - show coastal areas that are near a
large mango plantation.
• Map 3 - show coastal areas that have high
population densities for bad fishermen
Definition and Components of GIS
MAP 1
Areas with good coral reefs….
Definition and Components of GIS
MAP 2
coastal areas near large mango plantations….
Definition and Components of GIS
MAP 3
Areas with high densities of bad fishermen
Definition and Components of GIS
The analysis produces…...
• MAP 4 - intersection areas in all the 3 maps
produced earlier will show the areas that are:
– having coral coverages > 50%
– near dynamite sources
– near areas with high density of bad fishermen
• these are unsuitable areas for reef reserves…
Definition and Components of GIS
MAP 5
Areas unsuitable for reef reserves
Areas suitable for reef reserves
Definition and Components of GIS
SPATIAL PLANNING
• as a result of the analysis one can judge
whether an area is suitable (high possibility
of success) for the establishment of a
marine sanctuary or not……planning
• the design of the plan also specifies where
in the environment what interventions
should occur - an outline of the future
situation
Definition and Components of GIS
IMPLEMENTATION OF THE
PLANS
• plans are executed
• not anymore controlled by the GIS but can
be monitored by it….. which leads us to the
management aspect
Definition and Components of GIS
SPATIAL MANAGEMENT
• monitoring…. wherein changes are
recorded and attention is paid that no major
disturbances occur
• degree of destruction is closely watched
Definition and Components of GIS
DATA STRUCTURES
• data always refers to a location on the
surface of the earth expressed in a local or
global co-ordinate system
• data has to be digitally stored for a
computer to be able to read it
Definition and Components of GIS
WHERE & WHAT
• description of the world can be done in
geographical terms (where are the
objects),
• or in thematic expressions (what are the
objects)
*a meaningful description of the real world in its spatial
manifestation always contains both.
Definition and Components of GIS
DISTINCTION BETWEEN
SEMANTICS AND SYNTAX
• content (what?) • convention (how?)
• the meaning • the format
• what it represents in • how it is stored in the
reality computer
Definition and Components of GIS
“Ich mag GIS”
“Ganahan ko sa GIS”
“Four added to five makes ten”
“Fayb added to fayb makes ten”
Definition and Components of GIS
2 MAJOR DATA SYNTAXES
RASTER or GRID
&
VECTOR
Definition and Components of GIS
RASTER or GRID
• a “grid” of a uniform
pattern is put over
area to be described
• to each element a
value is attributed
• with a regular
structure - position
of each element can
be defined in relation
to the rest
Definition and Components of GIS
VECTOR
• structure points are
recorded in co-
ordinates and these are
connected to lines (the
vectors)
• a number of vectors
can be joined to form
polygons (areas)
• considers objects
Definition and Components of GIS
3 object types
• point - geometric description only refers to the
position of the object by a pair of coordinates
(x, y); used for trees, posts etc.
• line - geometrically described by recording the
coordinates of a series of points and the
sequence in which these points should be linked
(1D; eg., roads, canals, rivers)
• polygon - a line with the same start and end,
usually refers to an enclosed region (2D; eg.,
lakes, ponds, farm plots)
Definition and Components of GIS
A Line in…………………..
raster vector
Definition and Components of GIS
row = 1
column = 1
data = 1
row = 2
column = 1
data = 0
row = 3
column = 3
data = 1
a raster line……..
Definition and Components of GIS
start position
(x1, y1)
may also be
a function
end position
a vector line ……. (x2, y2)
Definition and Components of GIS
RASTER vs VECTOR
• FILE SIZE • larger • smaller
• SPEED • faster • slower
• LINKING • easier • A bit more
DATA difficult
• ACCURACY • ? • ?
Definition and Components of GIS
VECTOR overlaying RASTER
Definition and Components of GIS
